This invention relates to electric circuits for activating an occupant safety device responsive to an acceleration sensor in an automotive vehicle.
It is well known to activate a safety device such as a safety-belt tightener or an airbag, for example, only when a collision of the vehicle with another vehicle or an obstacle occurs. As a rule, acceleration sensors are used to detect such collisions by responding to the deceleration of the vehicle upon impact with the obstacle and then closing an electric circuit which causes the activation of a belt tightener or inflation of airbags.
Particular importance is attributed to protection in the event of a lateral collision, since there is insufficient space to provide a satisfactory path for energy-absorbing vehicle deformation in the region of sidewalls and/or doors, in contrast to the vehicle's front or rear area. Accleration sensors arranged to detect lateral collisions must respond very quickly so that the corresponding occupant safety device can become fully effective within the short period of time between the first contact of the sidewall with the obstacle and penetration of the sidewall into the passenger space. On the other hand, the electric activating circuit for the device should be designed so that it only activates the occupant safety devices if a collision which would imperil the occupants in the absence of such device actually occurs. If an acceleration sensor provided as a component of the activating circuit is located in the door of the vehicle, this means that any acceleration caused by other factors should not be effective to trigger the occupant safety device, which, in such cases, is generally a lateral airbag. Such noncollision-related accelerations are produced not only during normal operation of the vehicle, for example, by irregularities in the rolling surface, but also by forceful slamming of the door, or by the door hitting a lightpole or tree when opened. Such events may indeed produce accelerations having a magnitude which approaches those caused by collisions.
It is true that such accelerations are of very short duration, but detection of the duration of the acceleration cannot be used to differentiate such accelerations from those caused by collisions, since the time delay required for such detection would also delay the response of the occupant safety device in the event of an actual collision, with extremely harmful consequences.